Split locking piece for circumferential dovetail on turbine wheel

ABSTRACT

A turbine wheel includes a circumferential dovetail for retaining a plurality of circumferentially mounted turbine buckets. The circumferential dovetail includes a reduced dovetail portion or bucket admission slot for admitting the buckets onto the turbine wheel. A split locking piece is positioned in the bucket admission slot for closing the same after all the buckets have been mounted onto the turbine wheel. The split locking piece includes a pair of oppositely disposed legs which straddle the turbine wheel at the bucket admission slot and include radially outward flanges which join to form a platform. A cap straddles the platform holding the two legs together while a radially outwardly extending pin secures the cap to the platform.

[llll 3,826,592 July 30, 1974 SPLIT LOCKING PIECE FOR Rankin 416/222 X Rubio et a 416/215 CIRCUMFERENTIAL DOVETAIL ON TURBINE WHEEL Inventor:

Primary Examiner-Everette A. Powell, Jr. [75] Robe" Rabom Ftchburg Mass Attorney, Agent, or Firm-John 1F. Ahern; James W.

Mitchell [73] Assignee: General Electric Company,

Schenectady, NY.

Dec. 18, 1972 [22] Filed:

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A turbine wheel for a rotating turbo-machine includesa disk which is fixed to and concentric with a rotatable shaft. The rim of the disk is formed with a dovetail onto which there are mounted a number of circumferentially arrayed, radially outwardly extending blades or buckets. The buckets are slipped onto the dovetail through a bucket admission slot comprising a reduced dovetail located within the'rim dovetail. After all the buckets have been mounted, onto the rim of the turbine wheel, the bucket admission slot is closed with a locking piece which thereafter prevents circumferential displacement of the mounted buckets. The prior art includes examples of such devices.

One example of a locking piece includes a U shaped member which is inverted radially inward to a straddle position over the rim of a turbine wheel at the bucket admission slot. Thereafter, at least one .hole is drilled, in the axial direction, through both legs and the bucket wheel disk. A locking pin is then inserted through the hole to secure the locking piece to the turbine wheel disk. Drilling axial holes for locking pieces in multi-stage rotors to the required accuracy and size and location is a costly operation. It is difficult to inspect and control and requires special fitting of pieces if rebucketing is-necessary.

Another locking piece in the prior art is found in U. S. Pat. No. 2,036,083, to Robinson, issued Mar. 31, 1936 and assigned to the assignee of the present invention. In this patent, the buckets immediately adjacent the bucket admission slot are provided with oppositely facing, axially extending notches. A U shaped block is disposed in a straddle position onto the bucket admission slot and retained thereon by a plate which is inserted into the notches formed in the buckets adjacent the bucket admission slot. In this manner the necessity of drillingaxial holes in the bucket wheel disk is obviated.

The U. S. Pat. No. 2,315,616 to Hall issued Apr. 6, 1943 discloses a split locking piece comprising two leg members joined at a radially outer location by a weld. The integrity of the weld cannot be visually inspected, requiring use of non-destructive testing equipment, and the use of a weld fora high temperature turbine environment may result in failure of the weld.

Another example of the prior art is disclosed in U. S. Pat. No. 2,844,355, to Rankin, issued July 22, 1958 and assigned to the assignee of the present invention. In that patent, the locking piece is formed by a pair of radially inner blocks, one on each side of the bucket wheel, which are held in place by axial pins cooperating with adjacent buckets and a single radially outer block which is retained in a similar manner.

Finally. U. S. Pat. No. 3,084,343 to Rubio et al., issued Apr. 2, 1963 and assigned to the assignee of the present invention, discloses a split-type locking piece wherein two halves straddle the bucket admission slot and they are joined at a radiallyouter portion by means of axially extending pins.

It is therefore one object of the: present invention to provide an improved locking piece which may be easily assembled and disassembled.

It is another object of the present invention to provide an improved locking piece which obviates the necessity of drilling holes through the turbine wheel.

It is another object of the present inventionto provide an improved locking piece which may be visually inspected.

Other objects and advantages will become apparent from the following description of the invention and the novel features will be particularly pointed out hereafter in the claims.

Summary of the Invention A turbine wheel includes a rim formed with a dovetail for retaining a plurality of circumferentially mounted turbine buckets. A bucket admission slot is formed within the dovetail for mounting the turbine buckets onto the turbine rim. After the buckets have been mounted on the rim the slot is closed by means of a locking piece. According to the present invention the locking piece includes a pair of oppositely directed legs which straddle the bucket admission slot in a dovetail Brief Description of The Drawings FIG. 1 is a perspective view of a portion of a turbine wheel with an exploded view of the present invention applied thereto. 1

FIG. 2 is an elevation view of a portion of the turbine wheel, in section, taken at the bucket admission slot just forward of the locking piece according to the present invention. 1

FIG. 3 is a perspective view similar to FIG. 1 with the present invention removed so as to illustrate the bucket admission slot.

Detailed Description of The Invention Referring to FIGS. 1 and 3 of the drawings, a turbine wheel 11 is concentric and rotatable with a turbine rotor (not shown). The turbine wheel includes acircumferential rim having a dovetail 15. A plurality of turbine buckets 19 having root portions 23 with intersize positioned. within the circumferential dovetail 15,

of the turbine wheel.

The present invention is a split locking piece 41 as shown in FIGS. 1 and 2. The locking piece comprises a pair of legs 45a and 45b, opposite one another, and straddling the bucket admission slot. Each leg has an interior dovetail portion and a radially outer flange 46a and 46b and the two legs, assembled on the turbine wheel contact one another at a joint 47. The leg flanges when joined, form a platform 46 having a hole 51 therein. Each leg includes a groove or cut 55, parallel to the joint 47, the purpose of which will be apparent.

A pin 61, including a base 63, is positioned adjacent the rim of the turbine wheel in the bucket admission slot and extends radially outwardly therefrom through the hole 51 in platform 46 formed by the joined legs and their respective flanges. A rectangular cap 67 having a hole 71 therethrough and radially depending flanges 75 is positioned so that it abuts the platform 46 but is radially outward therefrom. The flanges are parallel to the joint 47 of the two legs and each flange abuts a respective groove 55. The radially depending flanges thus prevent the legs 45a and 45b from coming apart by securing them along the circumferential length of the platform. The pin 61 extends radially outwardly from the base 63 through holes 51 and 71 after which it is peened over thereby fixing the cap to the platform which in turn secures the two legs together. Each cap is also formed with a built-up portion 79 which resists bending stresses.

The assembly and operation of the invention is as follows. After all of the buckets have been entered on the turbine wheel by inserting them radially through the bucket admission slot and successively sliding them circumferentially, the slot is closed by the locking piece. Each leg of the locking piece is positioned on the turbine wheel starting at the radially inward positions and then joined so as to straddle the bucket admission slot. Before the legs are joined, the base of the pin is inserted between the wheel rim and the platform provided by the joined legs. The rectangular cap having the hole therethrough is positioned in abutment with the platform so that its radially depending flanges retain the sides of the legs along the circumferential length of the platform, thereby preventing the legs from coming apart. The pin extends radially outwardly from its base through both the platform and the cap, and, is peened thereby attaching the cap to the platform.

It should be appreciated that the present invention is simple to assemble and allows a visual inspection of the assembly. The present invention prevents circumferential movement of the turbine buckets by abutting the adjacent dovetail rim and may be easily disassembled for rebucketing. No drilling of the turbine Wheel is required. The interior dovetail portion of the joined legs is extensively machined to provide a lightweight construction thereby lessening the centrifugal forces operating on the dovetail joint when the machine is up to speed.

While there has been described herein what is considered to be the preferred embodiment of the present invention, other modifications will occur to those skilled in the art, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a turbine wheel including a rim formed with a dovetail for retaining a plurality of circumferentially mounted turbine buckets and having a bucket admission slot formed in said dovetail a locking piece inserted in said bucket admission slot for circumferentially retaining said buckets on said turbine wheel comprising:

a pair of oppositely disposed legs straddling said bucket admission slot in a dovetail fit and jointed to provide a platform radially outward from said wheel rim, said platform having a radially directed opening formed therethrough;

a cap adjacent said platform and radially outwardly therefrom having a radially directed opening therethrough in register with said platform opening; said cap further including radially depending flanges engaging the sides of said platform substantially along the circumferential length thereof; and,

fastening means having a radially inner portion, abutting the underside of said platform; and a radially outer portion abutting the top of said cap whereby said cap is secured to said platform.

2. The locking piece as recited in claim 1 wherein the platform includes a pair of grooves, one on each side of the platform along the circumferential length thereof for cooperatively engaging the depending flanges of said cap.

3. The locking piece as recited in claim 1 wherein the fastening means is a pin having an enlarged base at its radially inner portion and a peen at its radially outer portion. 

1. In a turbine wheel including a rim formed with a dovetail for retaining a plurality of circumferentially mounted turbine buckets and having a bucket admission slot formed in said dovetail a locking piece inserted in said bucket admission slot for circumferentially retaining said buckets on said turbine wheel comprising: a pair of oppositely disposed legs straddling said bucket admission slot in a dovetail fit and jointed to provide a platform radially outward from said wheel rim, said platform having a radially directed opening formed therethrough; a cap adjacent said platform and radially outwardly therefrom having a radially directed opening therethrough in register with said platform opening; said cap further including radially depending flanges engaging the sides of said platform substantially along the circumferential length thereof; and, fastening means having a radially inner portion, abutting the underside of said platform; and a radially outer portion abutting the top of said cap whereby said cap is secured to said platform.
 2. The locking piece as recited in claim 1 wherein the platform includes a pair of grooves, one on each side of the platform along the circumferential length thereof for cooperatively engaging the depending flanges of said cap.
 3. The locking piece as recited in claim 1 wherein the fastening means is a pin having an enlarged base at its radially inner portion and a peen at its radially outer portion. 